1. Technical Field
This disclosure relates to semiconductor fabrication and more particularly, to improved top layer imaging lithography wherein silicon is incorporated in an under layer to provide improved image quality.
2. Description of the Related Art
Semiconductor fabrication processes typically include photolithographic processing to pattern areas of a surface of a semiconductor device to form a protective layer over areas, preferably using a resist material. The protected areas remain during subsequent etching wherein the unprotected areas are etched away as needed. For top layer imaging, an image is formed by exposing and developing a thin imaging layer on the surface of a semiconductor device. The image created by exposing and developing the thin imaging layer is transferred to an under layer by an etching process where the top layer functions as an etch mask. The top layer or imaging layer that remains on the surface withstands the etch process and prevents etching in the protected areas.
After the first etch step, the resist or thin imaging layer is removed. The remaining portion of the under layer may now be used as a mask to etch a stack or substrate below the under layer. A subsequent etch step transfers the pattern of the under layer to the stack or substrate. Since the top layer is present during the under layer etching process, "grass formation" occurs on the top layer. Grass formation is the redeposition of silicon byproducts on the top layer as a result of etching the under layer. Grass formation typically results in a degradation of image transfer to the under layer from the top layer.
The top layer imaging technique also suffers from poor coating quality of the thin imaging layer. In conventional fabrication processes, the top layer performs two functions. First it provides an image to be transferred, and second it provides etch resistance to protect areas of the under layer while etching exposed areas of the under layer. These functions are balanced between image quality of the top layer and the etch resistance of the top layer.
Therefore, a need exists for a method which provides image transfer using an under layer to transfer the image. A further need exists for a method for providing improved coating quality using a high performance photoresist as a top layer by employing silylated portions of an under layer as an etch mask instead of the top layer.